Articular cartilage problems in the knee joint are common. Injured areas, called lesions, often show up as tear or pot holes in the surface of the cartilage. If a tear goes all the way through the cartilage, surgeons call it a full-thickness lesions. When this happens, surgery is usually recommended. However, these operations are challenging. Repair and rehabilitation are difficult. Your surgeon will consider many factors when determining the procedure that's best for you.

Articular cartilage is a smooth, slippery material that covers the ends of the bones that make up the knee joint. The articular cartilage allows the surfaces to slide against one another without damage to either surface.

The meniscus is a commonly injured structure in the knee. The injury can occur in any age group. In younger people, the meniscus is fairly tough and rubbery, and tears usually occur as a result of a forceful twisting injury. The meniscus grows weaker with age, and meniscal tears can occur in aging adults as the result of fairly minor injuries, even from the up-and-down motion of squatting.

What is a meniscus, and what does it do?

There are two menisci between the shinbone (tibia) and the thighbone (femur) in the knee joint. (menisci is plural for meniscus.)

The C-shape medial meniscus is on the inside part of the knee, closest to your other knee. Medial means closer to the middle of the body.) The U-shaped lateral meniscus is on the outer half of the knee joint. (Lateral means further out from the center of the body.)

These two menisci act like shock absorbers in the knee. Forming a gasket between the shinbone and the thighbone, they help spread out the forces that are transmitted across the joint. Walking puts up to two times your body weight on the joint. Running puts about eight times your body weight on the knee. As the knee bends, the back part of the menisci takes most of the pressure.

By spreading out the forces on the knee joint, the menisci protect the articular cartilage from getting too much pressure on one small area on the surface of the joint. Without the menisci, the forces on the knee joint are concentrated onto a small area, leading to damage and degeneration of the articular cartilage, a condition called osteoarthritis.

Surgeons use an arthroscope (mentioned earlier) during surgery for an injured meniscus. Small incisions are made in the knee to allow the insertion of the camera into the joint.

Knee Arthroscopy of Articular Cartilage Injuries

Arthroscopic Debridement

Surgeons use an arthroscope, a tiny camera inserted into the knee during surgery, to see into the joint and clean up the joint by trimming rough edges of cartilage and removing loose fragments. Sometimes this procedure is referred to as Chondroplasty. It is only intended to be a short-term solution, but it is often successful in relieving symptoms for a few years. This procedure is usually used when the lesion is too large for a grafting type procedure or the patient is older and an artificial knee is planned for the future.

Abrasion Arthroplasty

When osteoarthrities affects a joint, the articular cartilage can wear away, leaving bone rubbing on bone. This causes the bone to become hard and polished. During arthroscopy the surgeon can use a special instrument known as a burr to perform an abrasion arthroplasty. In this procedure, the surgeon carefully scrapes off the hard, polished bone tissue from the surface of the joint. The scraping action causes a healing response in the bone. In time new blood vessels enter the area and fill in with scar tissue (fibro cartilage) that is like articular cartilage. Fibro cartilage is weaker than normal articular cartilage. Because this is not true articular cartilage, it does not function as well for weight bearing as articular cartilage. The fibro cartilage that forms may not be strong enough to remove all the symptoms of pain in the knee. This usually is a temporary solution. Symptoms may return after this surgery.

Micro fracture

Surgeons use a blunt awl ( a tool for making small holes) to poke a few tiny holes in the bone under the cartilage. Like abrasion arthroplasty, this procedure is used to get the layer of bone under the cartilage to produce a healing response. The fresh blood supply starts the healing response and trigger the body to start forming new cartilage (mainly fibro cartilage) inside the lesion.

Post-Surgical Rehabilitation

Depending on the type of surgery, some surgeons have their patients use a continuous passive motion (CPM) machine to help the knee begin to move and to alleviate joint stiffness. This machine is used after many different types of surgery involving joints and is usually started immediately after surgery. The machine straps to the leg and continuously bends and straightens the joint. This continuous motion has been shown to reduce stiffness, reduce pain, and help the joint surface heal better with less scarring.

Many surgeons will have their patients take part in formal physical therapy after knee surgery for articular cartilage injuries. The first few physical therapy treatments are designed to help control the pain and swelling from the surgery. Physical therapist will also work with patient to make sure they are only putting a safe amount of weight on the affected leg.

With the exception of those who undergo a simple debridement, patients will be instructed to avoid putting too much weight on their foot when standing or walking for up to six weeks. This gives the area time to heal. People treated with an allograft are often restricted in their weight bearing for up to four months.

Patients are strongly advised to follow the recommendations about how much weight is safe. They may require a walker or pair of crutches for up to six weeks to avoid putting too much pressure on the joint when they are up and about.

Your physical therapist will choose exercises to help improve knee motion and to get the muscles toned and active again. At first, emphasis is placed on exercising the knee in positions and movements that don't strain the healing part of the cartilage. As the program evolves, more challenging exercises are chosen to safely advance the knee's strength and function.

Ideally, patients will be able to resume their previous lifestyle activities. Some patients may be encouraged to modify their activity choices, especially if an allograft procedure was used.

The physical therapist's goal is to help you keep your pain under control, ensure safe weight bearing, and improve your strength and range of motion. When you are well under way, regular visits to the therapist's office will end. Your therapist will continue to be a resource, but you will be in charge of doing your exercises as part of an ongoing home program.

Knee arthroscopy of Meniscus Injuries.

Partial Meniscectomy

The procedure to take out the damage portion of the meniscus is called partial miniscectomy. The surgeon makes a small incision. This opening is needed to insert surgical instruments into the knee joint. The instruments are used to remove the torn portion of the meniscus, while the arthroscope is used to see what is happening.

Surgeon would rather not take out the entire meniscus. This is because the meniscus helps absorb shock and adds stability to the knee. Removal of the meniscus increases the risk of future knee arthritis. Only if the entire meniscus is damage beyond repair is the entire meniscus removed.

Meniscal Repair

Whenever possible, surgeons prefer to repair a torn meniscus, rather than remove even a small piece. Young people who have recently torn their meniscus are generally good candidates for the repair. Older patients with degenerative tears are not.

To repair the torn meniscus, the surgeon inserts the arthroscope and views the torn meniscus. Some surgeons use sutures to sew the torn edges together. Others use a special fasteners called suture anchors, to anchor the torn edges together.

Surgeons are beginning to experiment with different ways to replace a damaged meniscus. One way is by transplanting tissue, called an allograft, from another person's body Further investigation is needed to see how well these patients do over a longer period time.

Post Surgical Rehabilitation

Rehabilitation proceeds cautiously after surgery on the meniscus, and treatment will vary depending on whether you had a part of the meniscus taken out or your surgeon repaired or replaced the meniscus.

Patients are strongly advised to follow the recommendations about how much weight can be borne while standing or walking. After a partial menisectomy, your surgeon may instruct you to place a comfortable amount of weight on your operated leg using a walking aid. After a meniscal repair, however, patients may be instructed to keep their knee straight in a lock knee brace and to put only minimal or no weight on their foot when standing or walking for up to six weeks.

Patients usually need only a few physical therapy visits after menisectomy. Additional treatment may be scheduled if there are problems with swelling, pain, or weakness. Rehabilitation is slower after a meniscal repair or allograft procedure. At first, expect to see the physical therapist two to three times a week. If your surgery and rehabilitation go as planned, you may only need to do a home program and see your therapist every few weeks over a six-to-eight week period.